<!DOCTYPE html>
<html lang="zh-cn">
    <head>
        <meta charset="UTF-8"/>
        <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
        <title>Document</title>
        <style>
            .scrollWrapper {
                position: absolute;
                left: 0;
                right: 0;
                bottom: 0;
                top:0;
            }
            .bottomInput {
                position: absolute;
                bottom:0;
                left:0;
                right: 0;
            }
        </style>
    </head>
    <body>
        <div class="scrollWrapper">
            <div class="bottomInput">
                <input type="text" placeholder="input"/>
            </div>
        </div>
        <script>
            // 在输入框获取焦点, 键盘弹起后, 真的是一行代码
            var interval = setInterval(function() {
                document.body.scrollTop = document.body.scrollHeight
            }, 100)
        </script>
    </body>
</html>